I know how to increase the strength of tendons – take mysostatin. While blocking myostatin results in more muscle mass, it also results in stiffer but smaller and more brittle tendons. I believe this is due to myostatin playing a role in the growth of tendon fibroblasts, such that myostatin produces more collagen in the tendons (making them more elastic and resilient). See this paper by Chris Mendias. This will be a major issue for those athletes that wish to take myostatin inhibitors. Perhaps only with a targeted approach, allowing myostatin to reach the tendon fibroblasts but not the myocytes, will this result in a safe form of muscle enhancement.

As for bone, I don’t think there is a quick fix for strengthening bones without increasing brittleness. This is due to limitations of the hydroxyapatite ceramic that is used for vertebrate bones, I think. We might just have to move to an all-metal skeleton (if that every becomes possible).

As for the comment about bipedalism and running, I’d like to point out that ostriches can run at 75km/h with their two legs. That’s pretty fast (not as fast as a horse or cheetah though).